Abstract
Both higher-level cognitive factors and lower-level sensory factors influence reading speed. Previous work in our lab has identified visual-span size (the number of letters recognized with high accuracy without moving the eyes) as a sensory factor limiting reading speed. Here, we compare the effect of intelligence to the effect of visual-span size on reading speed. We also asked whether these cognitive and sensory factors have independent effects on reading speed. The trigram letter-recognition method was used to obtain a profile of letter recognition accuracy as a function of horizontal distance from the midline, and visual span was operationally defined as the area under this curve. Visual-span size and Rapid Serial Visual Presentation (RSVP) reading speed were measured in eleven native-English-speaking children (ages 10–14) and eleven adults (ages 18–20) with normal or corrected-to-normal vision. The letter size was 1° (x-height). Children also completed two subtests of the Wechsler Intelligence Scale for Children (WISC-IV). The Vocabulary subtest requires participants to give oral definitions of words, and the Block Design subtest of perceptual reasoning requires participants to replicate a geometrical design. Vocabulary score was a significant predictor of reading speed, explaining 51% of the variance. Block Design score was not a significant predictor of reading speed. Visual-span size was a significant predictor of reading speed in both children and adults, explaining 35% of the variance. The Vocabulary score and visual-span size were not independent predictors of reading speed, but were highly correlated (r = 0.74). Like vocabulary size, visual-span size can be expanded with practice. It is possible that this correlation between cognitive and sensory predictors of reading speed occurred because both vocabulary size and visual-span size increase with the amount of reading experience during childhood.
Supported by NIH Grant EY002934 (GEL) and Graduate Research Partnership Program Fellowship from the College of Liberal Arts, University of Minnesota (TMB).